As the areal density of media used in magnetic disk devices has increased, the size of the recording bits has fallen to several hundred nm or below, with recording bits being expected to become even smaller in the future. The problem of the thermal agitation of magnetic particles becomes significant in this size range, but it is thought that the problem can be solved by increasing the coercive force (Hc) of the medium. On the other hand, if the coercive force of the medium is increased, the write magnetic pole needs to be a narrow magnetic pole that can create a write magnetic field that is at least as strong as the coercive force of the medium. The magnetic material at the tip of the write magnetic pole therefore needs to have a higher Bs value (saturation magnetic flux density).
FeCo alloy is known as having a high Bs value of 2.45 T, but the magnetostrictive constant is high at λ=30 to 70×10−6 and it is difficult to realize soft magnetism with only a single layer of FeCo alloy. Therefore FeCo alloy cannot be used in this state as the magnetic material of the write magnetic pole. Permeability can be given as an index of soft magnetism, and when the permeability of a magnetic pole of a write head is low, the magnetism of the magnetic pole becomes unresponsive in an induction field of a coil corresponding to the waveform of the recording bits, so that there is deterioration in the resolution of recording bits and the desired write characteristics cannot be obtained.
As methods of solving this problem, there is a method that provides an underlayer as a buffer directly below a FeCo alloy film and new materials have been developed, such as by mixing in a small amount of additional elements into the alloy. As one example, a soft magnetic layer with a high Bs value of around 2.4 T using an FeCoN composition was reported in IEEE. Trans. Magn., Vol. 36, pp. 2506-2508, (2000). However, since it is difficult to control magnetic anisotropy with a single film of FeCoN, soft magnetism has been improved by forming the FeCoN layer on a permaloy (Ni80F20) underlayer or by a construction where the FeCoN layer is sandwiched between permaloy layers. It should be noted that the above report describes an embodiment where the thickness of the FeCoN layer is 0.1 μm, and it is unclear whether soft magnetism is achieved with a thickness of 0.1 μm or above. In addition, to increase the write magnetic field, it is necessary to form the high Bs film used at the tip of the magnetic pole at least 0.1 μm thick.
Also, in Japanese Laid-Open Patent Publication No. H10-270246, a material with soft magnetism such that an anisotropic magnetic field Hk>20 (Oe), resistivity ρ>50(μΩcm), and a Bs value>1.6T is disclosed as a granular alloy film where additional elements have been added to FeCo. However, to raise the resistivity to 50(μΩcm) or above, it is necessary to increase the included amount of non-magnetic elements added to the magnetic elements, so that the saturation magnetic flux density falls and it is difficult to achieve a high Bs value of 2.1 T or above.
In this way, the reality is that a soft magnetic material that has a sufficiently high Bs value for actual use as the magnetic material of a write magnetic pole of a magnetic head is yet to be provided. This invention was conceived in view of these problems and provides a magnetic material that exhibits soft magnetism with a Bs value of 2.2T or above at a thickness of 0.1 μm or above. It is an object of this invention to provide, by using this magnetic material as the magnetic material of a write magnetic pole, a magnetic head that can be favorably used to write data onto a high-density medium with a high coercive force.